Optimization-Based Neural Style Transfer algorithms rely on the rich
feature representations extracted by a pre-trained neural networks.
All works in this regime which I am aware of use VGG pre-trained
for ImageNet classification  [1]}. I will define
\(\Phi (X)^l\)  be the tensor of feature activations extracted from input
image \(X\)  by layer \(l\)  of network \(\Phi \) .
